1-Oxadethiacephalosporins have been synthesized from penicillins by Saul Wolfe et al.: Canadian Journal of Chemistry, Volume 52, 3996 (1974); and by total synthesis in Journal of Heterocyclic Chemistry, Volume 5, 779 (1968) by J. C. Sheehan and M. Dadic; German Patent Application OLS (Offenlegungsschrift No. 2,219,601 (1972); Journal of American Chemical Society, Volume 96, 7582 (1974) and Japanese Patent Application OPI (Kokai) No. 49--133,594 (1974) by B. G. Christensen et al.
The present inventors have found some promising 1-oxadethiacephalosporins and explored a method disclosed in our British patent application No. 46,759 filed Nov. 12, 1975.
However, all the methods referred to above were not practical, because of low over-all yield, some by-products separable only difficulty, and long steps to be elaborated.
In order to avoid the formation of stereochemical isomers as by-products, the present inventors conceived a stereoselective synthetic method for preparing said 1-oxadethiacephalosporins.
The method, the embodiment of this invention, is disclosed hereunder in this specification.